#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
struct ceva
{
    int x,y,d;
} v[100001];
int s[100001];
int comp(ceva A, ceva B)
{
    if(A.y==B.y) return A.x<B.x;
    else return A.y<B.y;
}
int Dmax;

int main()
{
    int n,i,dmax,j,z;
    f>>n;
    for(i=1;i<=n;i++)
        {f>>v[i].x>>v[i].y;
         v[i].d=v[i].y-v[i].x;}
    sort(v+1,v+n+1,comp);
     j=1;
    for(i=1;i<=v[n].y;i++)
    {
        s[i]=s[i-1];
        while(i==v[j].y)
        {
            z=v[j].y-v[j].x+s[v[j].x];
            s[i]=max(s[i],z);
            j++;
        }
    }
    g<<s[v[n].y];
    return 0;
}